1. Field of the Invention
The present invention relates, generally, to drill bits used for the drilling of oil and gas wells, and also relates to methods for manufacturing such drill bits. Such bits are used in drilling earth formations in connection with oil and gas exploration and production.
2. Description of the Prior Art
It is well known in prior art drill bits to use cutting elements having on one end thereof a polycrystalline diamond compact, generate referred to as a "PDC." The PDC material is typically supplied in the form of a relatively thin layer on one face of a substantially larger mounting body. The mounting body is usually a stud-like end configuration and typically is formed of a relatively hard material such as sintered tungsten carbide. The diamond layer may be mounted directly on the stud-like mounting body, or it may be mounted via an intermediate disc-like carrier, also typically comprised of sintered tungsten carbide. In any event, the diamond layer is typically disposed at one end of the stud-like mounting body, the other end of which is mounted in a bore or recessed in the body of the drilling bit.
The bit body itself is typically comprised of one of two materials. The body is either a tungsten carbide matrix or is made of various forms of steel. When the body is made of steel, the pocket for receiving the stud is usually in the shape of a cylinder to receive the cylindrically shaped stud of the cutter.
It has been well known in this art that when the bit body is comprised of a tungsten carbide matrix, the pockets can be formed in whatever shape is desirable. For example, in U.S. Pat. No. 4,200,159 to Eberhard Peschel et at., there is disclosure that the cutter body can be in the form of a cylinder as illustrated in FIG. 7 of that patent or can be in the form of a pin (see FIG. 14) or in the form of a cone as illustrated in FIGS. 15 and 16 of U.S. Pat. No. 4,200,159.
When using a so-called blade cutter, those in the art of steel bodied bits have usually machined the cylindrical pockets from the front of the blade, thereby limiting access to the center of the bit.
We have discovered that by using a PDC cutter having a center cylindrical section and a spherical section on one end away from the PDC cutter end, thus essentially being in the shape of a bullet, the cutter can be placed in a pocket conforming, at least in part, to the spherical end of the cutter. We are thus able to provide cutter locations in the center of the bit that have not been previously available to those in the art.